1. Technical Field
The present invention relates to flexible printed circuit boards, and particularly to a method for manufacturing flexible printed circuit boards.
2. Description of Related Art
Nowadays, flexible printed circuit boards, especially flexible printed circuit boards in a hollowed out form, also called embossed boards or windows boards in the art, are widely used in electronic products. Referring to FIG. 7, a flexible printed circuit board 1 in a hollowed out form is shown. The flexible printed circuit board 1 includes a copper layer 3 and two coverlays 4 on two opposite sides of the copper layer 3. The flexible printed circuit board 1 has a hollowed out portion 2. At the hollowed out portion 2, electrical traces formed with the copper layer 3 are naked and two opposite sides of the copper layer 3 are exposed. Thus, the electrical traces at the hollowed out portion 2 is capable of conducting electrical connection at both sides, i.e., the exposed two opposite sides of the copper layer 3 is available for electrical connection.
Generally, flexible printed boards in a hollowed out form are manufactured using a typical laminating method. Firstly, a sheet of coverlay with an opening defined therein is laminated on a surface of a sheet of copper foil. Secondly, electrical traces are formed with the copper foil in a series of processes including coating photoresist layer, exposing photoresist layer, developing photoresist layer and etching the copper foil. Thirdly, another sheet of coverlay with an opening defined therein is laminated on an opposite surface of the copper foil so that the two openings of the two coverlays align with each other. Thus the electrical traces formed with the copper foil are naked and exposed from the two openings of the two coverlays.
However, the typical method for forming flexible printed boards in a hollowed out form described above has the following disadvantages. First, because the method manufactures flexible circuit boards sheet by sheet, only one flexible circuit board can be manufactured using the method describe above each time. Thus, efficiency of manufacturing flexible printed circuit boards in a hollowed out form is low. Second, precise alignment of the two openings in the two coverlays is difficult, and the two openings of the two coverlays may be offset. Therefore, precision of the electrical traces exposed is low and quality of the flexible printed circuit board is unsatisfactory.
What is needed, therefore, is a method for manufacturing flexible printed circuit boards to improve quality and efficiency of manufacturing flexible printed circuit boards in a hollowed out form.